Re: INFO: rcu detected stall in sys_kill

From: Daniel Axtens
Date: Wed Dec 04 2019 - 18:34:11 EST

Hi Casey,

> There haven't been Smack changes recently, so this is
> going to have been introduced elsewhere. I'm perfectly
> willing to accept that Smack is doing something horribly
> wrong WRT rcu, and that it needs repair, but its going to
> be tough for me to track down. I hope someone else is looking
> into this, as my chances of finding the problem are pretty
> slim.

Yeah, I'm having a look, it's probably related to my kasan-vmalloc
stuff. It's currently in a bit of flux as syzkaller finds a bunch of
other bugs with it, once that stablises a bit I'll come back to Smack.

Regards,
Daniel

>
>>>
>>> I see 2 common this across all stalls:
>>> 1. They all happen on the instance that uses smack (which is now
>>> effectively dead), see smack instance here:
>>> https://syzkaller.appspot.com/upstream
>>> 2. They all contain this frame in the stack trace:
>>> free_thread_stack+0x168/0x590 kernel/fork.c:280
>>> The last commit that touches this file is "fork: support VMAP_STACK
>>> with KASAN_VMALLOC".
>>> That may be very likely the root cause. +Daniel
>> I've stopped smack syzbot instance b/c it produces infinite stream of
>> assorted crashes due to this.
>> Please ping syzkaller@xxxxxxxxxxxxxxxx when this is fixed, I will
>> re-enable the instance.
>>
>>>> rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
>>>> (detected by 1, t=10502 jiffies, g=6629, q=331)
>>>> rcu: All QSes seen, last rcu_preempt kthread activity 10503
>>>> (4294953794-4294943291), jiffies_till_next_fqs=1, root ->qsmask 0x0
>>>> syz-executor.0 R running task 24648 8293 8292 0x0000400a
>>>> Call Trace:
>>>> <IRQ>
>>>> sched_show_task+0x40f/0x560 kernel/sched/core.c:5954
>>>> print_other_cpu_stall kernel/rcu/tree_stall.h:410 [inline]
>>>> check_cpu_stall kernel/rcu/tree_stall.h:538 [inline]
>>>> rcu_pending kernel/rcu/tree.c:2827 [inline]
>>>> rcu_sched_clock_irq+0x1861/0x1ad0 kernel/rcu/tree.c:2271
>>>> update_process_times+0x12d/0x180 kernel/time/timer.c:1726
>>>> tick_sched_handle kernel/time/tick-sched.c:167 [inline]
>>>> tick_sched_timer+0x263/0x420 kernel/time/tick-sched.c:1310
>>>> __run_hrtimer kernel/time/hrtimer.c:1514 [inline]
>>>> __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1576
>>>> hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1638
>>>> local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
>>>> smp_apic_timer_interrupt+0x109/0x280 arch/x86/kernel/apic/apic.c:1135
>>>> apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
>>>> </IRQ>
>>>> RIP: 0010:__read_once_size include/linux/compiler.h:199 [inline]
>>>> RIP: 0010:check_kcov_mode kernel/kcov.c:70 [inline]
>>>> RIP: 0010:__sanitizer_cov_trace_pc+0x1c/0x50 kernel/kcov.c:102
>>>> Code: cc 07 48 89 de e8 64 02 3b 00 5b 5d c3 cc 48 8b 04 24 65 48 8b 0c 25
>>>> c0 1d 02 00 65 8b 15 b8 81 8b 7e f7 c2 00 01 1f 00 75 2c <8b> 91 80 13 00
>>>> 00 83 fa 02 75 21 48 8b 91 88 13 00 00 48 8b 32 48
>>>> RSP: 0018:ffffc900021c7c28 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
>>>> RAX: ffffffff81487433 RBX: 0000000000000000 RCX: ffff88809428a100
>>>> RDX: 0000000000000001 RSI: 00000000fffffffc RDI: ffffea0002479240
>>>> RBP: ffffc900021c7c50 R08: dffffc0000000000 R09: fffffbfff1287025
>>>> R10: fffffbfff1287025 R11: 0000000000000000 R12: dffffc0000000000
>>>> R13: dffffc0000000000 R14: 00000000fffffffc R15: ffff888091c57428
>>>> free_thread_stack+0x168/0x590 kernel/fork.c:280
>>>> release_task_stack kernel/fork.c:440 [inline]
>>>> put_task_stack+0xa3/0x130 kernel/fork.c:451
>>>> finish_task_switch+0x3f1/0x550 kernel/sched/core.c:3256
>>>> context_switch kernel/sched/core.c:3388 [inline]
>>>> __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
>>>> preempt_schedule_common kernel/sched/core.c:4236 [inline]
>>>> preempt_schedule+0xdb/0x120 kernel/sched/core.c:4261
>>>> ___preempt_schedule+0x16/0x18 arch/x86/entry/thunk_64.S:50
>>>> __raw_read_unlock include/linux/rwlock_api_smp.h:227 [inline]
>>>> _raw_read_unlock+0x3a/0x40 kernel/locking/spinlock.c:255
>>>> kill_something_info kernel/signal.c:1586 [inline]
>>>> __do_sys_kill kernel/signal.c:3640 [inline]
>>>> __se_sys_kill+0x5e9/0x6c0 kernel/signal.c:3634
>>>> __x64_sys_kill+0x5b/0x70 kernel/signal.c:3634
>>>> do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
>>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>> RIP: 0033:0x422a17
>>>> Code: 44 00 00 48 c7 c2 d4 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e
>>>> 0f 1f 84 00 00 00 00 00 0f 1f 40 00 b8 3e 00 00 00 0f 05 <48> 3d 01 f0 ff
>>>> ff 0f 83 dd 32 ff ff c3 66 2e 0f 1f 84 00 00 00 00
>>>> RSP: 002b:00007fff38dca538 EFLAGS: 00000293 ORIG_RAX: 000000000000003e
>>>> RAX: ffffffffffffffda RBX: 0000000000000064 RCX: 0000000000422a17
>>>> RDX: 0000000000000bb8 RSI: 0000000000000009 RDI: 00000000fffffffe
>>>> RBP: 0000000000000002 R08: 0000000000000001 R09: 0000000001c62940
>>>> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000008
>>>> R13: 00007fff38dca570 R14: 000000000000f0b6 R15: 00007fff38dca580
>>>> rcu: rcu_preempt kthread starved for 10533 jiffies! g6629 f0x2
>>>> RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
>>>> rcu: RCU grace-period kthread stack dump:
>>>> rcu_preempt R running task 29032 10 2 0x80004008
>>>> Call Trace:
>>>> context_switch kernel/sched/core.c:3388 [inline]
>>>> __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
>>>> schedule+0x181/0x210 kernel/sched/core.c:4155
>>>> schedule_timeout+0x14f/0x240 kernel/time/timer.c:1895
>>>> rcu_gp_fqs_loop kernel/rcu/tree.c:1661 [inline]
>>>> rcu_gp_kthread+0xed8/0x1770 kernel/rcu/tree.c:1821
>>>> kthread+0x332/0x350 kernel/kthread.c:255
>>>> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
>>>>
>>>>
>>>> ---
>>>> This bug is generated by a bot. It may contain errors.
>>>> See https://goo.gl/tpsmEJ for more information about syzbot.
>>>> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>>>>
>>>> syzbot will keep track of this bug report. See:
>>>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>>>>
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